The resist material generally used heretofore is a polymer-based resist material capable of forming an amorphous thin film. For example, a resist thin film formed by coating a solution of a polymer-based resist material such as polyalkyl methacrylate (e.g., polymethyl methacrylate) and acid-dissociable reactive group-containing polyhydroxystyrene on a substrate is irradiated with an ultraviolet ray, a far ultraviolet ray, an electron beam, an extreme-ultraviolet ray (EUV), an X-ray or the like, whereby a line pattern having a line width of approximately from 45 to 100 nm is formed.
However, the polymer-based resist material has a large molecular weight of approximately from 10,000 to 100,000 and a broad molecular weight distribution and therefore, in the lithography using a polymer-based resist material, roughness is generated on the fine pattern surface, making it difficult to control the pattern dimension and leading to reduction in the yield. Thus, the conventional lithography using a polymer-based resist material as the main component has a limit in refinement. In order to produce a finer pattern, various low-molecular-weight resist materials which can be used as the main component are disclosed (see, for example, JP-A-2009-173625 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2009-173623, JP-A-11-258796 and Adv. Mater., 20, 3355 (2008)).
For example, JP-A-2009-173625 and JP-A-2009-173623 have reported a low-molecular-weight resist material composed of a calixarene derivative. In both reports, a pattern is formed using an alkali developer, that is, a positive pattern is formed in JP-A-2009-173625 and a negative pattern is formed in JP-A-2009-173623.
Also, JP-A-11-258796 has reported a low-molecular-weight resist material composed of a fullerene derivative, and it is indicated that a negative pattern is formed by irradiating the exposed area with an electron beam to cause chemical crosslinking and performing development using an organic solvent-containing developer.
Furthermore, Adv. Mater., 20, 3355 (2008) has reported a case of forming a positive pattern through EUV exposure and alkali development by using a low-molecular-weight resist material composed of a polynuclear phenol derivative.
These low-molecular-weight resist materials are expected to realize high resolution and excellent roughness characteristics thanks to their low molecular weight (small molecular size), but sufficient performances are not obtained so far. Among others, in the formation of an ultrafine pattern, it has been difficult to satisfy the resolution, line edge roughness (LER) and good dry etching resistance at the same time.
On the other hand, in recent years, a pattern forming method using a resist composition containing an acid-decomposable polymer material and a compound capable of generating an acid upon irradiation with an actinic ray or radiation and using an organic solvent-containing developer is also being developed (see, for example, JP-A-2008-281975, JP-A-2010-139996, JP-A-2010-164958 and JP-A-2009-25707).
For example, in JP-A-2008-281975, JP-A-2010-139996, JP-A-2010-164958 and JP-A-2009-25707, a pattern forming method including a step of subjecting a resist composition containing a polymer material having a relatively high content of a repeating unit containing a group capable of decomposing by the action of an acid to produce a polar group, to development using an organic solvent-containing developer is described. It is indicated that according to such a method, the roughness performance, dimensional uniformity and the like in forming an ultrafine pattern are excellent.
However, formation of an ultrafine pattern is difficult due to use of a polymer-based resist material as the main component and because a polar group is produced in the pattern area, the dry etching resistance needs to be improved.